1. Technical Field
The present disclosure relates generally to surgical interference screws and, more particularly, to surgical interference screws constructed from bone and adapted to compress soft tissue, e.g., ligaments, tendons, etc., against bone in a bone tunnel.
2. Background of Related Art
Surgical interference screws for attaching soft tissue, such as ligaments and tendons, to bone are well known. Typically, because of the relatively large amount of torque that must be applied to an interference screw during insertion, these screws are constructed from metal. The use of metal screws, however, sometimes necessitates surgical procedures for screw removal. Moreover, metal screws have a tendency to loosen and/or back out of a previously formed bore and result in bone loss.
Interference screws have also been constructed from bioabsorbable polymers, e.g., polyglycolic acid polymers. The degradation time of such polymers is selected to coincide with the healing time of the tissue being repaired. Typically, after degrading, bioabsorbable polymers leave acetic acid deposits which may lead to bone degradation and inflammatory reactions in the adjacent tissue.
Another problem associated with using interference screws formed from a bioabsorbable material is that the bioabsorbable material is likely to have a significantly lower strength and cannot be subjected to the high torque required for insertion. The distal region of a bioabsorbable screw is particularly susceptible to shear failure due to excess torque.
Screws made of human or animal bone are also known. For example, U.S. Pat. Nos. 5,968,047 and 5,868,749 issued to Thomas M. Reed disclose screws made from cortical and cancellous bone. Reed""s bone screws include a head portion configured to engage a driver. The head portion, for example, may include a hexagonal recess, a cruciform recess or philips recess to receive a drive tool. One problem associated with screws made of bone is that bone has a tendency to split or fracture at the interface with the driver tool. This problem is aggravated when using a driver that exerts expansion forces on the screw, such as a driver for engaging a screw having a hexagonal recess or a philips head.
Accordingly, a need exists for an improved surgical screw which can remain in the body after insertion, does not adversely effect adjacent tissue and has the requisite strength characteristics to be inserted into bone without fracturing. Moreover, a need exists for an insertion tool for inserting bone screws which stabilizes the screw at the screw/tool interface to prevent fracture of the screw during screw insertion.
In accordance with the present disclosure, an interference screw for surgical use is provided which is formed from bone, such as the ridge of the tibia. The interference screw includes an elongated body having a proximal end adapted to engage a screw insertion tool and a distal insertion end. The insertion end is tapered to facilitate entry into a bone tunnel formed in the bone. A bore extends through at least a portion of the elongated body. Insertion tool engaging structure is formed along at least a portion of the bore. The insertion tool engaging structure extends within the bore along a substantial portion of the length of the elongated body. In one embodiment of the presently disclosed interference screw, the proximal end of the interference screw includes a hexagonal head portion and the insertion tool engaging structure includes hexagonal walls defining the bore. The hexagonal walls extend from the proximal end of the elongated body distally to the point at which the tapered insertion end of the elongated body begins to taper. The outer surface of the elongated body also includes a helical thread which extends from the head portion to the distal end of the elongated body.
In another preferred embodiment of the interference screw, the elongated body includes a helical thread that extends from the proximal to the distal end of the elongated body. The insertion tool engaging structure also includes hexagonal walls defining the bore. The hexagonal walls extend over a substantial portion of the length of the elongated body and are configured to engage an insertion tool. In yet another preferred embodiment, a slot is formed in the elongated body through the hexagonal walls. The slot and the hexagonal walls extend from the proximal end of the elongated body to the point at which the insertion end of the elongated body begins to taper.
The interference screw is suitable for surgical use and may be used to secure soft tissue against bone. Typically, during an ACL reconstruction procedure, a bone-patellar tendon-bone graft (BPTB) is taken from the central ⅓ of the patient""s patellar tendon. Therefore, the reconstructed ACL is actually part of the patellar tendon with two blocks of bone on either end, from the patella and the tibial tuberacle. One of these blocks of bone is actually what gets placed inside the bone tunnel and fixed in place with an interference screw. The soft-tissue structure is intimately and biologically attached to the bone block, but it is actually the block of bone that gets compressed inside the tunnel. However, interference screws can also be used to wedge tendons against bone. Such a procedure would include an anterior cruciate ligament (ACL) reconstruction procedure. Interference screws are also used to attach bone against bone, not (Oust) soft tissue against bone. By constructing the screw from bone, several advantages are achieved. For example, bone resorbs by biological remodeling, not by chemical means. As such, bone is replaced by bone as it resorbs. Thus, the loss of strength during the resorption phase is less and more predictable than with a resorbable polymer. Moreover, bone bonds to bone. The fixation of the interference screw is enhanced as bone grows directly on to the surface of the interference screw.
Fixation of the interference screw is enhanced by a biological bond, while metal and polymer screws must depend only on a mechanical interlock with bone.